1. Field of the Invention
The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium having excellent surface smoothness and superior electromagnetic conversion characteristics.
2. Disclosure of the Related Art
A conventional magnetic recording medium comprises a magnetic layer on one side of a non-magnetic support and a back coat layer on the other side of the non-magnetic support to enhance the running durability.
In recent years, increases in the quantity of data being recorded have resulted in demands for similar increases in the recording density of magnetic recording media. In order to enable increases in recording density, a recording wavelength continues to shorten, and the thickness of the magnetic layer continues to reduce.
As the thickness of the magnetic layer is reduced, any surface roughness of the support is reflected in the surface of the magnetic layer, causing a loss in the smoothness of the magnetic layer surface and a deterioration in the electromagnetic conversion characteristics. As a result, a non-magnetic layer is provided on the support surface, for example, as an undercoat layer, and the magnetic layer is then provided on this non-magnetic layer.
As increasingly shorter recording wavelengths are being used, it is desirable to provide a flatter surface to the magnetic layer in view of spacing loss.
Japanese Patent Laid-Open Publication No. 2001-84549 discloses a magnetic recording medium in which the number of concavities with a depth of 50 nm or greater in the surface of the magnetic layer, as measured by a non-contact type surface roughness meter, is 10 concavities per 46237.5 μm2 or less, and the maximum depth Rv is 100 nm or less.